The present invention generally relates to draft measurement devices, and more particularly, to a portable draft measurement device capable of retaining a fluid level indicative of a draft of a vessel.
Successful navigation of a vessel through a body of water requires the vessel""s navigator to know the draft of the vessel. The draft of the vessel is defined as a depth of water displaced by the vessel. The draft can be measured as a vertical distance from a water-line on a hull of the vessel where the hull breaks a surface of the water to a lowest point on a submerged portion of the hull. The draft of the vessel can change depending on the cargo and weight of the vessel. If the vessel is traversing dangerously shallow water the vessel may become grounded and perhaps catastrophically could become damaged, threatening the lives of the crewman and in the case of the Exxon Valdez, causing environmental problems. Accurate predictions for the vessel""s drafts are based upon draft readings taken at the time of the vessel""s certification inclining experiment, performed for compliance with regulatory agencies, such as the U.S. Coast Guard.
One known method of measuring the draft uses a measuring tape. The user extends the tape from the deck of the vessel into the water. The draft is determined by subtracting 1) the measured distance from the deck to the waterline from 2) the deck to the lowest point of the hull. Disadvantageously, using the measuring tape, the user leans over a side of the hull to see where the tape breaks the surface of the water.
This method is disadvantageous for several additional reasons. First, wave action at the surface of the water can make observation of the water-line difficult. Second, careful visual observation of the measurement indicia while leaning over the hull side is at least inconvenient, and can be dangerous when strong wave action causes the hull to rock to-and-fro. Third, strong underwater currents can cause movement and flexing of an immersed portion of the measuring tape, reducing the accuracy of any measurements taken.
A fluid level gauge for measuring the level of a fluid in a container tank is disclosed in U.S. Pat. No. 1,605,821. The gauge includes a vertical cylindrical shell and a buoyant fluid level indicator that rises and falls with a level of the fluid within the shell. An elongate lever 11 coupled to a top end of the shell and extending radially away from the shell, when rotated, fixes the indicator 7 in place so as to indicate a fluid level at the time the lever is rotated. This gauge suffers at least the following disadvantages as applied to draft determination. First, the gauge is not suited to an environment in which the fluid level experiences substantial fluctuations because the gauge fails to provide baffle structures to dampen fluid level fluctuations. Second, the gauge is not portable.
Accordingly, there is a need to accurately determine the draft of a vessel with a portable and durable device. There is a further need to accurately determine the draft of a vessel in the presence of wave action at the surface of the water and underwater turbulence. There is a further need to reduce the dangers and difficulties associated with carefully observing and measuring the vertical location of a water-line and the draft of a vessel, respectively.
An object of the present invention is to provide a portable and durable draft measurement device for accurately measuring the draft of a vessel.
Another object of the present invention is to provide a device for measuring the draft of a vessel, wherein an individual can carefully, safely and conveniently observe a water-line to determine the draft while the device is completely removed from the water in which the vessel is floating.
Another object of the present invention is to provide a device for measuring the draft of a vessel, wherein an observable level of water used to determine the draft is created by the device when the device is immersed in the water in which the vessel is floating, and then retained by the device when the device is removed from the water.
Another object of the present invention is to decrease the difficulty of taking draft measurements and increase the accuracy of draft measurements as compared to prior art devices by dampening fluctuations in an observable level of water used to determine the draft, the fluctuations arising from wave action, fluid surges due to hydrostatic pressure and underwater currents.
Another object of the present invention is to reduce alignment errors between a device for measuring the draft of a vessel and the draft of the vessel.
These and other objects of the present invention are provided by a device for measuring the draft of a vessel floating in a body of water. The device includes a durable, elongate, substantially transparent tube having an upper end, a lower end, and an interior volume between the upper and lower ends. The device advantageously includes a valve fixed to the lower end of the tube, and a resiliently biased valve actuator coupled with the valve and accessible through the upper end of the tube for selectively opening and closing the valve. Selectively opening the valve with the lower end of the tube immersed in the water in which the vessel floats, creates a level of water within the interior volume of the tube indicative of a water-line on the vessel. Selectively closing the valve preserves or retains the level of water within the interior volume, whereby the device can be removed from the water and transported to a location where the level of fluid can be conveniently, safely, and accurately observed as against a measuring tape observed through the tube. The device includes a resilient member to bias the actuator into a position corresponding to the closed position of the valve, and a resiliently biased lock to hold the actuator in a position corresponding to the open position of the valve. Such conveniences increase the ease with which an individual using the device can take draft measurements. The device includes interior and exterior fluidic baffles fixed proximate the valve which advantageously dampen fluctuations in the level of fluid within the interior volume when the valve is open. Also, an alignment spacer, and/or bubble levels fixed to an external portion of the tube, advantageously orient the tube parallel with the draft of the vessel.
The foregoing objects are also achieved by a portable draft measurement device that includes a tube having an upper end, a lower end, an interior volume, and indicia to indicate a level of fluid retained within the interior volume. The device also includes a valve fixed to the lower end of the tube. The valve has an open position placing the interior volume into fluid communication with a fluid when the lower end is immersed in the fluid to create the level of fluid within the interior volume. The valve has a watertight, closed position to thereby retain the level of fluid within the interior volume. The device also includes an actuator coupled to the upper end of the tube for placing the valve into the open and closed positions. The actuator includes a first resilient member biasing the actuator into a first position corresponding to the closed position of the valve. The actuator is displaceable from the first position to a second position against a bias of the first resilient member to place the valve into the open position.
The foregoing objects are also achieved by a method of measuring a draft of a vessel with the draft measurement device. The method includes immersing the lower end of the tube in a fluid and aligning the upper end of the tube with a calibration mark on the vessel indicative of a known draft. A level of fluid is created and retained within the interior volume of the tube. The draft of the vessel is determined using the level of fluid retained within the interior volume.
Still other objects and advantages of the present invention will become readily apparent to those skilled in the art from the following detailed description, wherein the preferred embodiment of the invention is shown and described, simply by way of illustration of the best mode contemplated of carrying out the invention. As will be realized, the invention is capable of other and different embodiments, and its several details are capable of modifications in various obvious respects, all without departing from the invention. Accordingly, the drawings and description thereof are to be regarded as illustrative in nature, and not as restrictive.